The accuracy values of the synovial fluid for the diagnosis of PJI with a cutoff value of IL-6 (1228.00), IL-4 (7.83), and IL-6/IL-4 (382.10) were 70.83%, 83.33%, and 89.05%, the sensitivities for the diagnosis of PJI were 91.30% (95 CI, 78.31%, 97.18%), 71.74% (95 CI, 56.32%, 83.54%), and 81.32% (95 CI, 71.78%, 88.72%), and the specificities were 52.00% (95% CI, 37.58%, 66.12%), 94.00% (95% CI, 82.46%, 98.44%), and 98.86% (95% CI, 93.83%, 99.97%), respectively. This evidence concerns the gene IL6 and juvenile polyposis syndrome.